The present invention is related to a string pulling head structure of a racket stringer. Each of the opposite faces of the string chucks and the chucking plates is formed with two parallel slots. An antiwear slat is disposed on one side of each of the slots to serve as the bottom of the slot. The slats are inclined by equal inclination angle but in reverse direction. The string pulling head structure can be made at lower cost.
FIGS. 5 and 6 show a string pulling head structure of a conventional racket stringer. The string pulling head structure includes a string pulling head 7 composed of a first string chuck 71 and a second string chuck 72 mated with each other and fixed with each other by screws. A first chucking plate 73 and a second chucking plate 74 defining therebetween a chucking space 75. Springs 76 are compressed between the first and second chucking plates 73, 74 for pushing the first and second chucking plates 73, 74 to respectively attach to the first and second string chucks 71, 72. Each of the attaching faces of the first and second chucking plates 73, 74 and the first and second string chucks 71, 72 is formed with two channels 77 with inclined bottoms. The channels 77 of the first and second chucking plates 73, 74 and the first and second string chucks 71, 72 are mated with each other to together define a space for accommodating multiple steel balls 8 therein. When the first and second chucking plates 73, 74 synchronously slide, due to the inclined bottoms of the channels 77, the steel balls 8 will press the first and second chucking plates 73, 74 outward. At this time, the chucking space 75 between the first and second chucking plates 73, 74 is minified for chucking the racket string.
The steel balls 8 can roll within the channels 77 of the first and second string chucks 71, 72 and the first and second chucking plates 73, 74 to press the first and second chucking plates 73, 74. In order to enhance the antiwear capacity, the first and second string chucks 71, 72 and the first and second chucking plates 73, 74 are made of steel. In addition, the bottom of the channel 77 is generally formed with a semispherical cross-section and has a certain slope. Referring to FIG. 7, the semispherical and inclined channels 77 are formed by means of a spherical milling cutter. Due to the limitation of the material of the first and second string chucks 71, 72 and the first and second chucking plates 73, 74 and the special shape of the milling cutter, each time the milling cutter can only mill the first and second string chucks 71, 72 and the first and second chucking plates 73, 74 by a depth not exceeding 0.25 mm. Otherwise, the spherical milling cutter will be damaged. Therefore, in actual processing, it takes seven or eight minutes to mill one semispherical channel 77 and replace the milling cutter as shown in FIG. 8. The conventional string pulling head structure totally has eight channels 77. Therefore, it will take about one hour for processing. In addition, it is quite hard to keep good quality of the channels 77 in processing. Accordingly, it is time-consuming to manufacture the string pulling head and the manufacturing cost is high.